The present invention relates to an improvement in compressed air, thermal tempering apparatus for sheets of glass wherein air blast means are employed to effect rapid cooling of the glass. In presently known constructions, the apparatus includes a pair of spaced plenum chambers, each, having a front plate through which a plurality of nozzles extend for directing air onto opposite surfaces of the sheet of glass.
In the case of a known device of this type, the nozzles are designed to be displaced axially of the front plate of the chamber and fixed in a position which is selected for the particular shape of the glass being tempered by means of a tightening device. This tightening device comprises one or more plates adapted to slide parallel to the front plate of the air plenum chamber. These plates are provided with holes aligned with the holes in the front plate of the tank for slidably receiving the nozzles. A construction of this type is disclosed in German Offenlegungsschrift 2456795. In operation, the nozzles are held in position by the shearing effect of the plates sliding one relative to the other. A disadvantage of this type of construction is that the holes provided in the fixed front plate of the plenum chamber and in the sliding plate must coincide very precisely in order to obtain a uniform tightening action on all the nozzles. Accordingly, the structure of these blast heads is precision engineered.